Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$25.67	13.339%	$29.0941	$29.09	$29.10	$29.10
Purchase #2	$206.78	3.293%	$213.5893	$213.59	$213.60	$213.60
Purchase #3	$216.39	13.166%	$244.8799	$244.88	$244.90	$244.90
Purchase #4	$200.89	7.783%	$216.5253	$216.53	$216.55	$216.50
Purchase #5	$6.92	9.692%	$7.5907	$7.59	$7.60	$7.60
Purchase #6	$64.39	7.209%	$69.0319	$69.03	$69.05	$69.00
Purchase #7	$76.86	11.673%	$85.8319	$85.83	$85.85	$85.80
7 purchase totals =	$797.90		$866.5431	$866.54	$866.65	$866.50